I already booked my ultra-Europe ticket which was a roundtrip from YVR to ZRH.
However, I am not sure whether I need to book for intra-Europe tickets for my visa application.
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In a nutshell, you don't need to buy anything (not even the ticket out of the Schengen area) but you need to credibly establish the purpose of your trip. And sometimes a reservation could help with that.
See Does Schengen visa proof of transport requirement include travel inside Europe? for a discussion of the underlying logic in a somewhat different context.